The thermal state of the northern rivers of Russia has undergone significant changes in the last 30–40 years due to climate warming, changes in water runoff. The purpose of this investigation is to ...study and explain only changes in heat flux, their long-term and spatial patterns in the northeast Asian part of Russia. Here, the heat flux of rivers is formed under the influence of climatic conditions, the altitude and latitude location of rivers, continuous permafrost, aufeis, glacial runoff and groundwater recharge, different water regime of rivers. An important feature of the research is the use of a large number of hydrological stations—145 and 231 gauging stations with data on water discharge and stream temperature, mainly from 1955 to 2012/2018. The abundance of data enabled to create unique maps of heat-flux and its deviations from the values of the base period. Empirical relationships between heat flux, on the one hand, and water runoff and water temperature, on the other, made it possible to improve the initial data, showed the leading role of water runoff in long-term fluctuations in heat-flux. However, climatic warming enhances the role of the temperature factor and transforms the relationship between water runoff and heat-flux, “shifting” them upwards. So far, these violations have not covered most of the gauging stations. The long-term “behavior” of heat flux is not unambiguous. Nevertheless, the period since the late 1980s is distinguished by higher values of heat flux. 20% of gauging stations demonstrate an increase in heat, compared to the previous period, by 10, 39% demonstrate an increase from 10 to 25%, 36% demonstrate >25%. Since the mid-second half of the 2000s, the heat flux of the rivers in the western part of the region has signs of stabilization and even a decrease. The reason is low water flow. A violation of the stationarity of the series in terms of dispersion (
F
-test) was found at 30% stations with reliable and long-term observations, mainly in the eastern part. Further changes in the heat flux of the regional rivers will depend on both changes in the river water flow and temperature. Within a year, almost all annual heat flux (90–95%) is generated in the summer months and has peaks in June and July. In the Vilyuy River basin, in the upper and middle part of the Kolyma River basin and on the coast of the Sea of Okhotsk, the proportion of summer months decreases to 65–90%. In addition to estimation of heat flux at the hydrological stations, the inflow of river waters into the mouths of the main rivers of the region and, in general, into the Arctic seas was assessed in various ways.
The Agrakhan Bay of the Caspian Sea is a unique hydrographic and environmentally valuable object at the mouth of the Terek River. At the beginning of the 20th century, it was a typical sea bay; ...however, by the 21st century, it lost the features of a marine area and a single water body and was divided into two parts with their specific hydrographic network, water regime, landscapes, biota, and anthropogenic load. Rehabilitation of the wetlands of the former sea bay requires urgent and scientifically grounded measures, as well as good knowledge of the causes and features of its rapid degradation and data on its current hydrological-morphological and hydroecological state. In 2018–2020, the authors carried out a series of field reconnaissance, geodetic, hydrometric, botanical, and hydrochemical works in this part of the mouth, created a network of stations, took numerous water samples and bottom soil samples, and analyzed them in laboratories. A vast array of data from Roshydromet (Russian Hydrometeorological Service) stations, as well as multi-temporal cartographic materials and satellite images, have been accumulated and studied; a multilayer GIS and various maps, empirical dependencies, diagrams, and graphs have been constructed; the results of studies by outside specialists have been considered. This study has made it possible to comprehensively describe the current state of the former Agrakhan Bay, build a depth map, a landscape map, a map of bottom sediments, a map of macrophytes, and a map of hydrochemical parameters, describe the water regime and water balance of the main water bodies of the former bay, determine the relationships between the main hydrological and morphological characteristics, etc. Patterns, causes, long-term stages, and parameters of the unfavorable morphodynamics of the Agrakhan Bay in the 20th century and at the very beginning of the 21st century have been studied. This has made it possible to justify measures for partial restoration of the hydrological and ecological potential of the water bodies of the former Agrakhan Bay.
The thermal state of the northern rivers of Russia has significantly changed during the last 30–40 years due to climate warming and changes in water runoff. The purpose of this study is to ...investigate and analyse these changes, their long-term and spatial patterns. In the northeast Asian part of Russia, including Chukotka, the northern districts of Yakutia and the Magadan Region, the thermal state of rivers is affected by cold climatic conditions, high altitudes, continuous permafrost, aufeis, glacial runoff and groundwater recharge. It is closely related to flow direction and dimension of rivers. The study uses dataset containing observations of river water temperature (mainly from 1955 to 2012/2018) at 231 gauging stations and records of 34 weather stations. The large dataset enabled to create seasonal and monthly air temperature maps, as well as maps of deviation of these parameters from the values of background period. The boundaries of ten altitude-thermal zones were set and for each zone a relationship between temperature and mean catchment height was established. Empirical relationships between water and air temperatures showed the leading role of air temperature in changes in stream temperature. It was found that, despite the huge size of the northeastern region and contrasting natural conditions, noticeable climatic warming (by 1–2°C) has been recorded almost at the same time (since 1988). To the east of the Indigirka River, it has been detected since the mid-1990s. The air temperatures increase in spring and autumn is higher than in summer when the main river heat-flux is generated. The beginning of the first noticeable increase in stream temperatures dates back to the late 1980s. The next time milestones were the mid-late 1990s, the first half of the 2000s (from the Indigirka River to the Anadyr River), the late 2000s–early 2010s (western part of the region). The rivers and territories with positive water temperature anomalies predominate. The average range of anomalies is from ‒0.2 to +1.5°C; extreme values are from ‒0.8 to +2°C. The Arctic rivers, the area at the intersection of the Vilyuy and Olenek river basins, and the rivers to the east of the Kolyma River have maximum positive water temperature anomalies. Observed trends create favorable conditions for the intensification of thermal erosion and an increase in turbidity of river water.
The article provides an overview of publications devoted to assessing changes in the water regime of Russian rivers under the conditions of current and projected climate changes. The most recent ...summary of the relevant publications is contained in the national assessment reports of Roshydromet. Since the publication of these fundamental works, a large number of studies have been published, clarifying the conclusions of the national reports. The purpose of this review is to summarize the modern ideas about the impact of climate change on the territory of the Russian Federation on the mean annual and maximum river flow, primarily based on the publications in recent years. The review is divided into two parts. The first part presents the results of the diagnosis of changes in the long-term norms of the annual and maximum flow of Russian rivers that occurred during the period of instrumental observations in the XX–early XXI centuries. Due to the geographical differences in the direction and magnitude of climate changes and associated changes in the water regime of rivers, the review is given separately for the rivers of the European and Asian territories of Russia. It is shown that the annual runoff over the territory of European Russia in recent decades has a tendency to increase, associated with a general rise in the humidity of the territory. However, for most of the analyzed river basins, the changes are statistically insignificant. The annual runoff of rivers from the territory of Siberia and the Far East into the Arctic seas of Russia has also slightly increased on average. The changes in the maximum runoff are more pronounced and differently directed. The second part of the article provides an overview of publications that present projections of changes in the water regime of Russian rivers until the end of the XXI century. The projections were obtained in ensemble experiments with climate models or with regional hydrological models. The conclusions made in the Second Assessment Report of Roshydromet regarding the insignificant positive anomalies of the annual runoff rate for most of the territory of Russia under moderate anthropogenic warming scenarios in the XXI century have been confirmed. The most pronounced positive anomalies of the snowmelt and rainfall runoff in the XXI century are possible on large rivers of Siberia in the case of implementation of the RCP8.5 scenario of anthropogenic radiation impact.
The inundation situations on the Black Sea coast of the Krasnodar territory for the period from 1945 until 2013 were analysed and the main types of inundations at the coast are described. Synoptic ...factors of the formation of extreme precipitation and rainfall floods, features and regularities of the downstream flood wave transformation in the rivers are also studied. Therefore, assessments of seasonal and maximum flow of the Black Sea coast rivers for the period of hydrometric measurements were done. Regularities of change of the occurrence of inundations and their characteristics on the coastal terrain were analysed, for a year and on a perennial timescale. Most catastrophic and exceptional inundations arise in the summer and in early autumn. Small inundations during the remaining year reflect the seasonal distribution of river flow and floods in the Black Sea rivers. Extensive and sometimes extreme precipitation dominates the river flow regimes. The seasonal distribution of small and moderately dangerous inundations reflects, on average, a water regime of two groups of rivers of the coast – to the north and to the south of the Tuapse River. To the north of the Tuapse River, floods prevail from November until March (up to 70 % of observed floods took place in this period) as a result of precipitation and winter snowmelt during frequent thaw periods. In winter, high waters often overlap to form a multi-peak high water of 2–3 weeks' duration. In the summer and in early autumn we observe a steady low flow. The total amount of runoff increases both in a southeast direction, and with the altitude of the river basins. Interannual variability of mean annual runoff, as well as maximum runoff, on the contrary decreases in the southern direction and with an increasing area of the river basins. The coastal high waters of the rivers of the Sochi part of the coast are typical at any time of the year, but more often floods in the cold season result from incessant rain, and thawing snow. Annually up to 25 floods have been observed. The principal reason of such distribution is the increase of extreme rainfall in the warm season. Orographic features of the coast and detailed features of rainfall only cover a small number of local river basins and a limited area. The geographical correlation of individual rainfall and subsequent floods ceases to be statistically significant for distances over 40–60 km. The annual flow cycle is mainly determined by two seasons, winter/spring and summer, with strong and weak flows, respectively; almost 71 % of all catastrophic and exceptional inundations took place in July–August (71 %) and in October–November (29 %). The characteristic features of dangerous floods are their rapid formation and propagation, a significant increase of water level (up to 5–7 m and more) and the multiple increase of water discharges in comparison with low flow period. Analysis of the interannual changes of the number of inundations at the Black Sea coast of the Krasnodar territory has shown some increase of the number of inundations in the period from the early 1970s until the early years of the twenty-first century. Quantitative assessments of risk, hazard and damage for the population and economic activities from accidental inundations in the valleys of the Black Sea coast rivers show that economic and social losses from inundations at the Black Sea coast of the Krasnodar territory are some of the highest in the Russian Federation. The basic conclusion from recent inundations is the need to consider not only the lower reaches and mouths of the Black Sea coast rivers where the main part of the social and economic development of the coast is concentrated, but also whole river basins and catchments. Further, an analysis of the efficiency of the measures applied at the coast to mitigate inundations and their after-effects is provided.
Abstract
The study was based, firstly, on the diverse data collected during field work in 2018 – 2020 in the eastern part of the Terek River delta and long-term hydrological monitoring data on the ...Roshydromet gauges. Secondly, on a profound comparative analysis of multi-temporal cartographic materials and multiple satellite images, laboratory analysis of water and sediment samples and other research groups’ field data. The performed analysis resulted in unprecedented complex and profound assessment of the contemporary hydrological, morphological and ecological state of the former Agrakhan Bay of the Caspian Sea. The drivers, dependencies and parameters of hydrological and morphological degradation were described; a multi-layer large-scale GIS was created to design multiple illustrations. The performed assessment allowed for development of measures for partial restoration of the hydrological and ecological potential of the former Agrakhan Bay.
Lena flow showed considerable, mostly climate-induced, changes in the recent 30–40 years. The character of these changes at the river watershed–sea border somewhat differs from that in the basin ...outlet station because of flow transformations in the near-mouth reach and, especially, in the delta. The new stationary and occasional expedition observations were used to improve the estimates of the major characteristics of the discharges of water, suspended sediment, and heat in the Lena outlet section and to identify the features and causes of their long-term and seasonal variations. Another important result is the estimation of flow characteristic in the reach downstream of the basin outlet station, at delta head, and on its coastline. New data are given on the present-day distribution of water and suspended sediment discharges between the major delta branches, their long-term variations, and the character of inundation of the near-head delta area during spring floods.
We analyse inundation situations on the Black Sea coast of Krasnodar territory for the period from 1945 until 2013 and describe the main types of inundations at the coast. Synoptic factors of the ...formation of extreme rainfalls and rainfall floods, features and regularities of the downstream flood wave transformation in the rivers are studied. Assessments of seasonal and maximum flow of the Black Sea Coast rivers for the period for which hydrometric measurements describe regularities of change of the occurrence of inundations and their characteristics on the coastal terrain, within a year and on perennial time scale. Most catastrophic and exceptional inundations arise in the summer and in early autumn. Small inundations during the remaining year reflect the seasonal distribution of river flow and floods in the Black Sea Rivers. Extensive and sometimes extreme precipitation dominates the river flow regimes. The seasonal distribution of small and moderately dangerous inundations reflects, on average, a water regime of two groups of rivers of the coast - to the north of the Tuapse River, and to the south. To the north of the Tuapse River, floods prevail from November until March (to 70 %). They result from precipitation and winter snowmelt during frequent thaw periods. High waters in the cold season of the year often overlap with each other, forming a multipeak high water with 2--3 weeks in duration. In the summer and in early autumn a steady low flow is observed. The total amount of runoff increases both in a southeast direction, and with the altitude of the river basins. Inter-annual variability of mean annual runoff, as well as maximum runoff, on the contrary decreases in the southern direction and with an increasing area of a river basin. The coastal high waters of the rivers of the Sochi part are typical at any time of the year, but more often floods in the cold season result from incessant rains, and thawing snow. Annually up to 25 floods are observed. The principal reason of such distribution is the increase of extreme rainfalls in the warm season. Orographic features of the coast and detailed features of rainfall cover only a small number of local river basins and a limited area. The geographical correlation of individual rainfall and subsequent floods ceases to be statistically significant for the distances over 40--60 km. The annual flow cycle is mainly determined by strong winter and spring, and weak summer flows: Despite a characteristic distribution of floods and of water flow within a year, almost 71 % of all catastrophic and exceptional inundations took place in July -- August (71 %) and in October -- November (29 %). The characteristic features of dangerous floods are their rapid formation and propagation, a significant increase of water level (up to 5-7 m and more) and multiple increase of water discharges. An appreciable increase of the number of inundations in the period from the early 1970s until the early years of the 21.sup.th century was noted. Quantitative assessments of risk, hazard and damage for the population and economic activities from accidental inundations in the valleys of the Black Sea coast rivers show that economic and social losses from inundations at the Black Sea coast of the Krasnodar territory are one of the highest in the Russian Federation. The basic conclusion from recent inundations is the need to consider not only the lower reaches and mouths of the Black Sea coast rivers where the main part of the social and economic development of the coast is concentrated, but also total river basins and catchments. Further, we provide an analysis of the efficiency of the measures applied at the coast to fight inundations and their aftereffect.
Regularities in the response of the mouths of major rivers, flowing into the Caspian Sea, to large-scale variations in its level and river water runoff and sediment yield are considered. Changes in ...the morphological structure and hydrological regime of the Volga, Terek, Sulak, Ural, and Kura mouths have been analyzed in both geological past and separately for three modern periods: a considerable drop in Caspian Sea level before 1978, its abrupt rise in 1978–1995, and a relative stabilization in the subsequent years. Specific features were identified in the hydrological-morphological processes in different mouths, caused by the differences in river sediment yields, and the slopes of delta surface and mouth nearshore beds. Some theoretical and methodological approaches were verified in the analysis and evaluation of the processes under consideration. The obtained results of studies of the mouths of rivers flowing into the Caspian Sea can be regarded as examples and analogues in the assessment of processes, which take place at the mouths of other Russian and world rivers at present and can take place in the future under anticipated natural and anthropogenic variations in sea level and river runoff.
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